Modified or sustained release pharmaceutical dosage forms have long been used to optimize drug delivery and enhance patient compliance, especially by reducing the number of doses of medicine the patient must take in a day. The use of sustained release dosage forms has increased due to dosing convenience and potentially reduced adverse effects. Multiple-unit sustained release dosage forms have been used for the delivery of therapeutic agents due to their inherent clinical advantages over single-unit dosage forms. These dosage forms spread out uniformly in the gastrointestinal tract and potentially reduce the risk of local irritation and dose dumping, which are often seen with single-unit dosage forms.
Well known mechanisms by which a dosage form (or drug delivery system) can deliver drug at a modified rate (e.g. sustained or delayed release) include diffusion, erosion, and osmosis. An important objective of modified release dosage forms is to provide a desired blood concentration versus time profile for the drug. Fundamentally, the pharmacokinetic profile for a drug is governed by the rate of absorption of the drug into the blood, and the rate of elimination of the drug from the blood. To be absorbed into the blood (circulatory system), the drug must first be dissolved in the gastrointestinal fluids. For those relatively rapidly absorbed drugs whose dissolution in gastrointestinal fluids is the rate limiting step in drug absorption, controlling the rate of dissolution (i.e. drug release from the dosage form) allows the formulator to control the rate of drug absorption into the circulatory system of a patient.